Testing means for a primer



Jan. 15, 1957 H. w. STREET 2,777,323

TESTING MEANS FOR A PRIMER Filed May 28, 1952 FIG.1. FIG.2.

ELE c -gmc Fi; jfi mvswr v A: 67 HARRY W. L. STRE 53 54 68 I BY Q RA ATTORNEYS TESTING MEANS FOR A PRIMER Harry W. L. Street, Silver Spring, Md.

Application May 28, 1952, Serial No. 290,610

Claims. (Cl. 73-35) (Granted under Title 35, U. 5. Code 1952 sec. 266) This invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates in general to a timer and more particularly to a timing device for testing an explosive primer by the use of an electronic timing apparatus whereupon the sensitivity and potency of the explosive charge therein may be determined.

Heretofore, devices of this type have not proven entirely satisfactory for the reason that the contact element employed therewith for signalling the moment of impact with the primer failedto function instantly when the firing means for the primer was actuated. Furthermore, the probes disposed within the explosive flame were ineffective to close a circuit in the event that the explosive did not produce an appreciable ionization. Furthermore, with such devices in constant use and the firing of numerous primers therein the products of combustion therefrom often fouled the surfaces of the contacts and prevented proper electrical connection therebetween and the starting impulse would fail to reach the timer. Such devices also depend on anion current to develop a signal to stop the timer, the current being initiated by the ionized particles in the flame directed between a pair of probes as the explosive charge in the primer is fired.

In view of the foregoing, a new and improved device has been devised which overcomes all the aforesaid disadvantages for the reason that no mechanical restraint is placed on the firing device and the means for actuating the firing device to fire the primer and thus by this arrangement the timer is started instantaneously in response to an initial impact of the actuating means with the firing device. Furthermore, by the use of a capacity change to develop a signal for stopping the timer instead of employing ionic conduction, the device of the present invention will operate satisfactory by primer explosive mixtures which do not produce any detectable ionization.

The present invention contemplates the provision of a new and improved capacitor device for use with an electronic timing apparatus wherein the'time interval between the initial impact upon an explosive primer charge and the appearance of the flame therefrom is accurately measured. The invention also provides a device wherein a capacity change develops a signal in response to the initial impact received by the primer firing means which is transmitted to an electronic timer and serves to set the timer in operation and upon explosion of the primer by the firing means the products of combustion pass between the electrodes of a sensitive element and in response thereto a capacity change develops a signal which JCE proved capacity device for deriving signals which start and stop respectively an electronic interval timer.

Another object of the invention is the provision of a device for use with an electronic timer wherein means responsive to an initial impact received thereby develops a signal for starting the operation of the timer and in which means responsive to a flame from an explosive primer develops a signal for stopping the operation of the timer.

Another object of the invention is the provision of a signalling device wherein a capacitor actuated in response to an initial impact with a primer develops a signal which serves to start the operation of an electronic timer and in which a second capacitor responsive to the products of combustion of an explosive-charge of the primer develops a signal which serves to stop the operation of the timer.

A further object of the invention is to provide new and improved means employing a sudden capacity change to develop a signal which serves to start the operation of a timer when the firing means for a primer receives an initial firing impact and in which means responsive to a sudden flame received thereby as the primer is fired develops a signal which serves to stop the operation of the timer.

Still another object is the provision of new and improved means for measuring the thermal energy of the explosion of the primer.

Other objects and many of the attendant advantages of thi invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: I

Fig. l is an enlarged sectional view of the device of the present invention and a fragmentary portion of a conventional test set and illustrating the manner in which the device is supported thereon;

Fig. 2 is an enlarged plan view of the capacity probe employed with the device of Fig. 1;

Fig. 3 is an inverted plan view of the device of Fig. 2;

Fig. 4 is a sectional view taken on the line 4-4 of Fig. 2;

Fig. 5 is a sectional View taken on the line 55 'of Fig. 2; and,

Fig. 6 illustrates a schematic block and circuit diagram suitable for use with the device of Fig. 1.

Referring now to the drawings and more particularly to Fig. 1 thereof the reference character 10 indicates a fragmentary portion of a conventional primer test apparatus comprising a casing 11 having supported thereon the signalling device of the present invention and generally indicated by the numeral 12.

The casing 11 is provided with an opening 13 having arranged therein an annular support 14- composed of suitable insulating material such, for example, as hard rubber or the like, on which is formed a flange 15 in engagement with and secured to the casing 11 in any suitable manner, the support 14 being provided with a centrally disposed opening or bore 16.

A cup-shaped electrode generally indicated by the reference character 17 is supported by the member 14 and comprises a body member 18 disposed within the bore 16 and a flange 19 in engagement with the flange 15, the flange 19 providing supporting means for the electrode. The electrode has a conical portion 21 formed thereon which terminates in an end wall 22 and extends into the casing 11, the wall having a centrally disposed opening 23 formed therein.

Disposed within the casing 11 is a frame member indicated by the numeral 24 and comprising an annular rim member 25 forming a well 26. Integrally formed with the member 25 is a tubular sleeve 27 of reduced diameter with respect to the rim 25, the sleeve 27 being in engagement with a bracket 28 secured to the casing as at 29 and thus by this arrangement the frame 24 is supported on the casing 11 in alignment with the electrode 17.

A retainer 31 is arranged within the well 26 and comprises an annular flange 32 in abutting relation with the rim 25 whereupon the retainer is detachably maintained within the well 26. The retainer has formed thereon an end wall 33 in engagement with a shoulder 34 arranged on frame 24 at the junction of the rim 2S and the tubular sleeve, the wall having formed therein a centrally disposed opening 35 in alignment with the opening 23 in wall 22.

Arranged within the retainer and in substantial abutting engagement with the flange 32 is a primer holder or support generally indicated by the reference character 36 and comprising a relatively thick disk or mass 37 in which is formed a centrally disposed recess 38 in communication with an aperture 39, the aperture being somewhat smaller in size than the recess 38.

As more clearly shown on Fig. 1 a primer 41 is disposed within the recess 38 with the flange portion 42 thereof in engagement with the wall 33 of the retainer 31, the primer being adapted to be fired by a firing pin generally indicated by the reference character 43 in response to an initial impact received thereby. The impact sufiicient to fire the primer is developed by a mass in the form of a ball 44 as the ball is released from an initial position of rest and moves into a firing position shown in dashed outline on Fig. 1 and strikes the firing pin. It will be understood, however, that the diameter of the cup-shaped electrode is of suificient size to permit the ball to strike the firing pin without engaging or contacting the wall of the electrode 17.

The firing pin comprises a shaft 45 slideably arranged within a guide member 46 secured to the casing 11 as at 47. One end of the shaft 45 is loosely fitted within the opening 23 in the wall 22 of the electrode 17 and extends a predetermined amount therebeyond and thus by this arrangement the ball or mass 44 may readily strike and engage the protruding end portion of the firing pin as the ball is dropped into the cup-shaped electrode 17, the other end of the firing pin being reduced in diameter with respect to the shaft 45 thereof thereby to form a striker or impinging element 48. The striker is disposed within the aperture 39 in engagement with the primer 41, the striker being adapted to fire the primer as it is forcibly driven into engagement therewith in response to the initial impact of the ball 44 with the firing pin.

The aforesaid arrangement is employed to develop a signal to start the operation of the timer in response to the rapid increase in capacity between the insulated cup 17 and the frame 46 upon the initial impact of the ball with the firing pin and is electrically connected thereto by a conductor 51 secured to the electrode 17 as at 52 and a conductor 53 secured to the firing pin guide 46 as at 54, Fig. 1.

As clearly shown in Fig. l a thermojunction capacity probe generally indicated by the reference character 55 is supported in the tubular portion of the frame 24. The probe comprises a plug 56 composed of any insulating material suitable for the purpose such, for example, as Bakelite fitted into the bore 57 formed in the member 27 and maintained therein by a flange 58 integrally attached thereto and arranged in abutting engagement with the terminal end portion of the tubular member. A pair of normally spaced thermocouple terminals 59 and 60 are secured to the plug 56 in any suitable manner prefer ably as by being molded therein, the posts extending a predetermined amount beyond one end portion of the plug 56 with the terminal end portions thereof bridge by a thermocouple element 61.

As more clearly shown on Fig. 3 a cylindrical electrode 62 encircles the terminal end portions of the posts 59-69. and the bridge element attached thereto, the cylindrical wall of the electrode 62 being in predetermined spaced relation with respect to the terminals posts and the opening 35 in member 31. The cylindrical electrode 62 is supported by a terminal post 63 secured thereto as at 64 and to the plug 56 in any suitable manner such, for example, as being molded therein. By the aforesaid thermocouple arrangement and upon firing of the primer 41 by the firing pin 43, the products of combustion therefrom pass between electrode 59, cylindrical electrode 62 and the frame 46 of the timer thereby changing the capacity therebetween and thus developing a signal for stopping the operation of the timer. The electrical connection between the probe 55 and the timer being established by a conudctor 65 secured to the post 63 as at 66, con ductor 67 grounded to the casing or frame 11 as at: 68 and conductor 69 secured to the electrode 59 as at 71 and grounded to the frame as at 72.

Referring now to Fig. 6 for a more complete understanding of the present invention in connection with a conventional electronic timer device, the timer T and a pair of amplifier units A and A1 therefor are illustrated in block form thereon. The unit A is adapted to amplify the transient signal developed in response to the relatively large capacity variation resulting from the initial impact of the ball 44 with the firing pin 43 thereby to start operation of the timer and the unit A1 being adapted to amplify the signal developed as the capacity between post 59 and electrode 62 of thermocouple probe 55 is changed by the products of combustion from the explosive charge as the primer is fired, thereby to immediately stop operation of the timer.

it will be understood, that in response to the initial impact of the ball 44 with the firing pin 43 a sudden and rapid increase in the capacity between the cup-shaped electrode 17 and the frame 24- will occur. However, when the ball strikes the firing pin it also becomes effectively connected to the frame since the firing pin is grounded to the frame through the firing pin guide 46 and conductor 53. Furthermore, the cup-shaped electrode 17 is initially charged to a potential preferably of about 300 volts relative to the frame from a suitable source of electrical energy (not shown) by way of conductor 51. In response to the sudden change of capacity between the cup and frame, a sudden decrease of potential on the cup occurs as the ball strikes the firing pin and thus a transient signal is developed, which signal is amplified by the unit A and thus in response thereto the timer is set in operation. However, to prevent the relatively slow changes of potential occurring on cup electrode 1.7 when the ball enters the. cup and approaches the firing pin from being amplified by the amplifier unit A, suitable mcans are employed such, for example, as a condenser and resistance filter network (not shown), the time constant thereof being relatively short, for example, in the order of one microsecond.

The probe arrangement 55 for developing a signal to stop the operation of the timer functions as the explosive flame is detected and is electrically connected to the timer by conductors 65, 67 and 69. The circular electrode 62. however, is adapted to be charged to a potential of about 300 volts by way of conductor 65 from a suitable source of electrical energy within the amplifier. Furthermore, since the thermocouple probe 55 is arranged in alignment with the primer 41 and opening 35 it will be understood that when the primer is fired by the firing pin the products of combustion from the explosive charge therein are directed toward the probe 55 and pass between the componcnts parts thereof and the frame. When this occurs the resulting change of the dielectric constant causes a change of capacity between the cylindrical electrode 62 and the frame causing a change in the potential on the post 63 whereupon a signal is developed, the signal being amplified by the unit A1 and serves instantly to stop the operation of the timer.

The thermocouple element 61 is connected by way of post 6t)v to a voltmeter 70, preferably of the type known in the art as a peak voltmeter, from whence the circuit is continued to ground. An arrangement is thus provided in which the voltage generated by the thermocouple junction is employed to operate the voltmeter in response to the heat applied to the thermocouple by the explosion of the primer under test. The thermal capacity of the junction is large enough so that the temperature of the junction reaches only a small fraction of the flame temperature. The junction temperature is therefore proportional to the integral of the flame temperature with respect to time and thus a visual indication is given of the thermal energy of the explosion. With this arrangement the condition of the primer with particular reference to the effectiveness of the explosive material is made manifest.

In view of the foregoing, it will be understood that the present invention provides a new and improved detection and signalling device suitable for use with an electronic interval timer and having a capacitor arrangement, the capacitance of which is instantly changed in response to the initial impact of a metallic mass with the primer firing means thereby to develop a signal which serves to start the operation of the timer, and in which a second capacitor arrangement is employed, the capacitance of which is changed suddenly by a flame from the detonator explosive thereby to develop a signal which serves to stop the operation of the timer. Furthermore, by the aforesaid arrangement means are provided whereby a reliable and accurate measurement of the time interval between the initial impact received by the primer firing means and the appearance of the flame from the explosive charge therein is efi'ected. Variations of the time interval between initial impact and the appearance of the flame from a plurality of primers under test may be employed to determine the sensitivity of each primer tested and in surveillance tests this information serves to indicate the rate of aging of the explosive charge in the primers.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent in the United States is:

1. A device of the character disclosed for testing an I explosive primer, the combination of primer firing means, a mass for driving said firing means into firing engagement with a primer, a normally charged cupshaped electrode having an aperture within which said firing means is adapted to move without contact with the electrode, and an electronic timer having a starting connector connected to said electrode for developing a timer starting signal resulting from an increase in the capacity between the electrode and firing means as the mass moves within said electrode an amount sufiiciently to drive said firing means into firing engagement with the primer.

2. A device of the character disclosed for testing an explosive primer, the combination of a frame, a normally grounded firing pin movable within said frame from an initial position to a firing position, an initially charged cup-shaped electrode insulated from said frame and having an aperture within which said firing pin is adapted to move to said firing position without contact with said electrode, a mass movable within said cup-shaped electrode for driving said pin to said firing position, an electronic timer having a pair of starting and stopping connections, said electrode being connected to said starting connection for applying thereto a timer initiating signal correlative to a change in capacitance occurring between said electrode and said firing pin upon impact of said mass with the pin, the impact of said mass with the pin being suflicient to drive the pin to said firing position, an annular electrode carried by said frame and disposed adjacent a primer which is ignited by said pin when in said firing position and being within the path of the explosive flame emitted therefrom, a thermocouple assembly insulatably arranged within said annular electrode and disposed in the path of said flame, said annular electrode and thermocouple assembly forming the electrode plates of a capacitor having an initial capacitance therebetween which capacitance is varied upon impingement thereon of said flame thereby developing a timer terminating signal, said annular electrode being electrically connected to said stopping connection for applying thereto said timer terminating signal whereby the timer is stopped.

3. A device of the character disclosed for testing an explosive primer, the combination of firing means re-, sponsive to an initial impact received thereby for firing a primer, a movable spherical mass for applying said impact to said firing means, a normally charged cupshaped capacitor having an aperture within which said firing means moves to engage and fire a primer without contact with said capacitor, and an electronic timer having a starting connection connected to said capacitor and rendered effective to start the timer by an increase in the capacity between the capacitor and firing means when said mass enters the cup-shaped capacitor an amount sufficiently to apply said initial impact to said firing means.

4. In a device of the character disclosed for testing an explosive primer, the combination of an electronic timer having a starting connection, a firing chamber, a firing pin slideably arranged within said chamber for firing a primer as the pin is moved into firing engagement therewith in response to an initial impact received thereby, a movable spherical mass for applying said impact to said firing pin, a normally charged cup-shaped capacitor secured to said chamber and insulated therefrom, said capacitor having an aperture therein within which said firing pin moves to firing engagement with said primer without contact with said capacitor, said capacitor being connected to the starting connection for developing a timer initiating signal in response to an increase in capacity between the cup and pin when the mass moves within said capacitor an amount sufficiently to apply said initial impact to said pin.

5. A device of the character disclosed for testing a primer, the combination of an electronic timer having a starting and stopping circuit therein, a casing, a firing pin included in said starting circuit and having a ground connection to said casing, said firing pin being adapted to fire a primer as the pin is forcibly driven into firing engagement therewith, a movable spherical mass for driving said pin into firing engagement with a primer as the mass strikes the firing pin, and a normally charged cup-' shaped electrode included within said starting circuit, said electrode having an aperture within which said firing pin moves to engage a primer without contact with said electrode, said mass being adapted to cause a sudden increase in the capacity between said electrode and said pin when the mass enters said electrode an amount sufficiently to strike said pin thereby to develop a signal to start the timer at the instant of said impact.

References Cited in the file of this patent UNITED STATES PATENTS 1,241,213 Heisler Sept. 25, 1917 1,922,320 Olin et al. Aug. 15, 1933 2,011,710 Davis Aug. 20, 1935 2,395,902 Nisewanger Mar. 5, 1946 2,434,349 Cohen Jan. 13, 1948 2,508,996 Elam May 23, 1950 2,519,421 Weiss Aug. 22, 1950 2,525,020 Jarlais Oct. 10, 1950 2,564,596 Dahline Aug. 14, 1951 2,575,922 Langenwalter Nov. 20, 1951 2,602,110 Jones July 1, 1952 

